1. Field of the Invention
The invention relates to MOS devices and somewhat more particularly to a process of reducing density of fast surface states in MOS devices, such as surface-charge-coupled devices (SCCDs).
2. Prior Art
In surface-charge-coupled devices, for example as described by C. H. Sequin et al, Charge Transfer Devices, Academic Press Inc., New York, pages 11 and 12, (1975), low surface state densities at Si-SiO.sub.2 interface regions are of primary importance in regards to transmission properties (and dark currents) associated with such devices.
Normally, the production of MOS devices comprises a careful gate oxidation followed by hydrogen annealing in a gas atmosphere. B. E. Deal, "The Current Understanding Of Charges In The Thermally Oxidized Silicon Structure", J. Electrochem. Soc., Vol. 121, No. 6, pages 198C through 205C (1974) suggests that hydrogen saturates so-called "dangling" bonds at Si-SiO.sub.2 interface regions in semiconductor structures. During such saturation, the dissociation of the H.sub.2 molecules into atomic hydrogen is of primary importance. This saturation occurs during annealing in a hydrogen atmosphere at a temperature in the range from about 400.degree. C. to 500.degree. C. over a time period of about 30 minutes. Surface state densities which can be achieved by means of this process are about (5-10).times.10.sup.9 cm.sup.-2 eV.sup.-1. In the case of SCCDs this means a transfer loss, .epsilon., of about (1-2).times.10.sup.4, which is inadequate for many applications.